As for the prior art, one can refer to, for example, HITACHI HYORON, Vol. 65, No. 10 (October 1983), pp. 23-28. In a device disclosed by this reference, a disk is rotated at a constant angular velocity and there is used, as a data recording system, a pit position recording system in which "1" of code information after modification corresponds to the center of a pit. Also, the device employs a CAV (constant angular velocity) system in which the recording bit rate is constant over all circumferences of the disk. Accordingly, a bit length on the disk is different between inner and outer circumferences. For example, if the radius of the outermost circumference is twice as long as that of the innermost circumference, the bit length on the outermost circumference becomes twice as long as that on the innermost circumference. In the CAV system, the characteristic of a recording/reproducing system may be constant since the recording bit rate is the same over all circumferences. Also, the number of sectors per one track may be the same irrespective of the inner and outer circumferences of the disk.
In the case where it is desired to obtain a higher density than that in the CAV system, there can be considered systems as follows. A recording system as means for improving the linear recording density includes a pit edge recording system in which "1" of code information corresponds to the edge portion of an elongated hole or pit. In this system, it is possible to detect an edge position from a reproduced waveform even in the case where the linear recording density is made high as compared with that in the pit position recording system even if the characteristic of an optical system is the same. Further, if the pit edge recording system is used in combination with an MCAV (modified CAV) system in which the linear recording density is substantially constant over all circumferences of the disk and the rotating speed of the disk is made constant, it is possible not only to improve the linear recording density by virtue of the pit edge recording but also to attain a large capacity without bringing about the lowering of an access speed. When the radius of the outermost circumference is twice as long as that of the innermost circumference, the use of the MCAV system makes it possible to improve the capacity up to about 1.5 times as large as that in the CAV system. In order to use the pit edge recording system and the MCAV system in combination, there is required a track/sector format which is different from the conventional format used in the combination of the pit position recording system and the CAV system.